Does urban “green” harbor healthier microbes?

We evolved in natural environments, characterized mainly by soil, water, vegetation, and the innumerable microorganisms associated with each. Many researchers have observed linkages between human well-being and exposure to green space, including mental restoration, reductions in disease and mortality, better birth outcomes, and decreased crime and violence. Explanations for why these benefits are observed are often based on the idea that humans are evolutionarily predisposed to prefer environmental settings that confer survival advantages, namely landscapes that are similar to the savannas and woodlands that humans are thought to have inhabited for thousands of years. Is it possible that vegetation is a source of the microbes we have co-evolved with over the millennium and whose presence we may require for physical and psychological health?

Westernized societies are plagued with increasing rates of auto-immune disorders. A recent study in New York City has shown that kids in neighborhoods with more street trees are less likely to have asthma, after controlling for socioeconomic factors. Several other research studies have found that children exposed to higher environmental diversity (i.e. living on a farm or forested rural setting versus living in a city) were exposed to higher microbial diversity and had lower rates of asthma and allergic disposition.

If we could quantify the relationships among human health, microbial diversity and urban green space, would it change the way we design cities? Should we put a higher priority on providing adequate green space for all urban residents? Majora Carter says, “Race and class are extremely reliable indicators as to where one might find the good stuff, like parks and trees, and where one might find the bad stuff, like power plants and waste facilities.” How can planners and designers ensure that all city residents will have a positive and equitable microbial experience as they interact with the invisible urban microbiome?

May 24 2013:
A different way to think about cities and urban planning could be through the lens of ecosystem services, both provided for and by cities. Ecosystem services are the processes and conditions through which natural ecosystems help sustain human life. They are usually divided into categories: Provisioning services (products such as food and water obtained from ecosystems), Regulating services (benefits from regulation of ecosystem processes like regulation of water and climate), Supporting services (services necessary for other ecosystem services, e.g. cycling of oxygen, water and nutrients) and Cultural services (non-material benefits obtained through ecosystems). If urban planners begin to focus on cities in such a context, that could help cities become more sustainable and improve the quality of life for people in the cities.
An example is water cycling. Water is vital for life on Earth but climate change is predicted to change precipitation cycles, likely requiring communities to plan for floods and droughts. More impermeable surfaces mean that water can’t naturally go into soil, where it can become purified, potentially leaving more water with a higher concentration of pollutants. Urban green (parks, trees, green roofs) would allow for more water to enter soil, purify itself, and re-enter the water cycle. Also, soil biodiversity and quality are linked to water regulation and purification. Planning cities to allow for the cycling of water could increase people's quality of life, and provide for the soil and biodiversity surrounding the city, which would help the growth of plants and other crops used for human consumption. I think seeing cities as one, important part of a much larger ecosystem will be necessary in the future city planning to make cities sustainable in the face of climate change and population growth.
Jannson 2013 Ecological Economics 86:285-291 http://www.sciencedirect.com.libproxy.uoregon.edu/science/article/pii/S0921800912002388

If microbial community diversity were confirmed to have a human health benefit, it would be interesting to suggest that maintenance of that diversity through urban green space is also an ecosystem service.

May 24 2013:
I agree that looking at the ecosystems services provided by green spaces is an excellent idea, and I think many cities are starting to implement this change. In regards to water filtration, I have noticed throughout Portland, many parking lots, for example the Fred Meyers on Hawthorne, have been reconstructed to include bioretention cells (depressed areas covered by vegetation to allow for filtration and infiltration), and the EPA has a page dedicated to better storm water management that include green roofs, the elimination of curbs, and permeable pavement, all of which could be beneficial to alleviate some precipitation stresses due to climate change.http://www.epa.gov/oaintrnt/stormwater/best_practices.htm

I particularly liked Christine's comment about considering cities a part of a larger ecosystem, and while looking at the benefits ecosystem services provide us, adding green spaces allows us to provide services to many of the species that are currently being threatened by our urban sprawl. With the current declines in biodiversity we are facing worldwide it is important to try to alleviate this as much as possible when planning for future development. Green spaces if designed correctly can provide stepping stones for migratory birds, and other animal populations allowing them to persist in developed areas. The Audubon Society is currently implementing a program to provide urban oases for migratory song birds.

May 22 2013:
Green roofs are a potentially great way to introduce green space into already developed cities, but what about equal access? Those who are likely to be able to afford creating a green space are also more likely to be able to afford getting out of the city to areas with more green space. Thus, my question is this how might a planner want to incorporate/tackle this issue of wanting to develop green spaces in a city with little open space to develop so all would have access and the benefits (e.g. health and aesthetically speaking)?

May 22 2013:
That is a good question, even in that other discussion I don't think anyone had considered the impact of bees on the urban microbiome.

I almost think that in this case, the impact of the urban microbiome on bees may be a larger concern than the impact of bees on the urban microbiome. Surely bees have their own endemic microbes, but cities already have a substantial insect population, so I'm not sure how much bees could contribute to the present urban microbial cloud, especially in a way that affects human health. However, with all the concerns of colony collapse threatening bees, it may be wise to examine the health and robustness of bee colonies already in cities (Paris is apparently an urban bee hotspot). Also studying whether making bees more cosmopolitan and widely spread will increase the spread of bee diseases and parasites, and if this significantly negatively impacts their well-being.

May 22 2013:
I think this just supports the need for more green space in urban areas, especially if we are incorporating urban beehives. I think it is also important to construct the green spaces with native vegetation, so that the pollinators are matched with the species they have co-evolved with, this would maximize benefits to the flowers and the bees

May 22 2013:
In Eugene, it was only recently that we were even allowed to build green roofs. THere are now specs for green roof construction and these have to have a permit and pass inspection. Portland is well ahead of us in the progression of moving toward more green building practices. They are like our older sibling and we follow their lead.

May 22 2013:
Wow Ben you flipped it. So this makes me think about the impact of the urban microbiome on the health of urban gardens and urban spaces. I wonder if there is a link? I wouldn't be surprised.

May 22 2013:
In addition to green roofs, some countries are also incorporating green walls into their city design. In 1994, Toronto displayed an indoor green wall that was used for bio-filtration. It might be interesting to consider adding indoor green walls inside hospitals to increase healthy microbial diversity. I think the more green space included in urban areas the better, and including them in building code is a great idea

May 25 2013:
Sandra, check out these green walls: http://gsky.com/green-walls/. This is also in response to a comment by Ben. This technology will allow for further development of green space in cities so it won't be limited to roof tops. Plus the amount of diversity that can occur with these walls has the potential to significantly expand the urban microbiome because of how many green walls can be added throughout a city.

May 22 2013:
The first thing to understand for any city planner that wanted to improve the "green" in a city would be how far the effect of microbial "gardens" reached? Do the effects of a green area of the city reach people a mile away or 200 ft away? If money is spent in affluent areas to improve biodiversity does that reach people living in poorer areas?

May 22 2013:
Great point. We have been thinking about the BioBE Center http://biobe.uoregon.edu/ about the spatial distance of a person's microbial "aura". You are taking this to another level and thinking about the spatial distance of a green space "aura".

May 25 2013:
This comment highlights the importance to make sure that the distribution of new green spaces are not clustered in only affluent areas, but they are distributed across a city so everyone can benefit from them.

May 22 2013:
Given what I've witnessed in Columbus, cities can make concerted efforts to add green space by including it in any redevelopment process. Most of the new construction/redevelopment around Columbus has included green roofs, tree-lined streets, parks, and mini gardens. All of these areas are not necessarily in affluent locations. Convincing the owner of every building to spend the money to develop a green roof may not be possible, when cities undergo redevelopment of a once non-green area, they have the ability to make it green regardless of the socioeconomic status of the people found in the area.

May 22 2013:
What do you think are the major factors that influence change in city planning? How much is scientific data used? Do you think that microbiome data, if it is ultimately shown to have strong links to health, would play a role?

May 23 2013:
I think both environmental sustainability and green spaces are becoming a prominent part of city planning because science has elucidated how our environment affects our physical and mental health, which in turn affects other factors such as crime rates. Local organizations such as Beyond Toxics (http://www.beyondtoxics.org/) in Eugene are working to reduce environmental/health risks due to pesticides and air pollution in low-income neighborhoods. They also have a “healthy bee” campaign that is working to create more pesticide-free garden areas in Eugene.
I think if there is a connection between microbial diversity and human health this will strengthen the argument for green spaces, in addition to the evidence that they may improve mental health and reduce obesity.

May 22 2013:
Since the trend seems to be packing more people into the city without expanding the boundaries how do we add green to the cities to improve microbial diversity? Would green roofs add enough "green" to improve diversity?

May 22 2013:
There was a talk at at the Ecological Society of America last year on microbes and greenroofs. They were studying soil microbes in greenroofs as compared to parks and found that in general the greenroofs did not contribute significantly to the microbial diversity. There was a possibility this was due to the recent introduction of greenroofs as compared to parks. http://eco.confex.com/eco/2012/preliminaryprogram/abstract_39736.htm

May 22 2013:
I'm realizing now though that the title of the abstract is about airborne diversity, whereas the content is about soils. Did the research team mention anything about this disjunct? I am wondering if they decided that the soils question was more important than the air question?

May 22 2013:
I don't know the correlation between soil and airborne microbes. However, there is significant variability in airborne microbes temporally as well as spatially. This study http://www.sciencedirect.com/science/article/pii/S016920460300197X by Fierer et al. in 2008 tried to understand the microbial diversity through time.

May 22 2013:
If we really are focusing on increasing the density of cities to prevent sprawl, I'm not sure if roofs alone would be enough green space (although they would certainly help!), with such a high concentration of people per area. Better placement of parks and more trees on streets could be another big contributor to making sure mroe people have ready access to green spaces and the health benefits they confer, be they microbial, psychological, or, more likely, a mix of both.
If cities really start to get dense enough, perhaps terraced gardens/parks in high rise buildings will become more widespread; I think these are already being experimented with in Italy.

May 22 2013:
Why are we trying to increase densities in cities and preventing urban sprawl in the first place? I guess a better question is how? Is it that people would rather live in the city then in a rural area? Or are we as a society trying to convince more and more people this is what we should do?

May 22 2013:
I'm not one of the most architecturally inclined, but my understand is that it's largely to increase people's proximity to things to allow more walkable cities, better public transport, and less need for cars. Also there is probably a goal of not spreading urban spaces further out than they need to be, for the sake of the environments that would be pushed out of the way.

May 22 2013:
The global population is expected to increase by more than a third in the next 30 years. In the US they are projecting a 79% increase in developed area. The exact amount varies by region, but that is a lot of land being converted from 'natural' area to development. http://www.sciencedirect.com/science/article/pii/S016920460300197X Denser cities could reduce this impact.

May 22 2013:
People usually want to live in cities for jobs, activities, better access to resources, etc. Living in a rural area isn't bad, but the sprawl element is an issue because of the amount of wasted resources/energy that result from urban sprawl. Not only is there the pollution issue of traveling, but in many locations where "sprawl" occurs, development has removed either critical farm land or ecosystems. The focus shouldn't just be on having people live in cities, but wherever people are living, have those cities develop in a sustainable way with their eyes towards the future and possible future population expansion. It seems many cities have been too focused on the now and not planning their cities accordingly for future population expansion.

May 22 2013:
Yes Janielle - spot on. I don't think it's only that we're trying to increase densities in cities. It's my understanding that the rise of megacities is happening whether we like it or not.

May 24 2013:
Green roofs are a great idea and provide so many benefits from storm water management to improving the costs of the heat island effect to aesthetic value. One perhaps often overlooked benefit is the opportunity to create thousands of new jobs. If 1% of the United States' roof space in communities where the population is over 50,000 were converted to Green Roofs, it would create 190,000 new jobs. (http://www.greenroofs.org/index.php/about/greenroofbenefits)

May 22 2013:
With the studies of city vs. rural kids I have to wonder how much diet was a factor.
I’m thinking rural kids are more likely to eat fruits and vegetables grown in microbe diverse healthy soil, were as city kids are likely eating fruits and vegetables grown in chemically treated soil.

As to auto-immune disorders there are much bigger factors then microbe health that contribute to the odds in getting one. (Low vitamin D due to poor diet and/or lack of sun, high stress, and in my case having “O-“ blood type.) So rather or not microbes is a factor, it weakens the agreement for healthy microbe environments when you hint there is a strong connection.

May 24 2013:
I completely agree with you that there are probably numerous different factors that might contribute to the rise in auto-immune disorders. I think it is an interesting question to think that maybe more microbial diversity might be better for us than less, since that idea conflicts with the hyper-sanitation trends. This paper has more information:

May 22 2013:
If data suggests a link between health and proximity to green space, the next hurdle will affecting policy that will not only benefit the wealthy. How will we make sure that an equal distribution of green space is developed in poor and wealthy communities?

May 22 2013:
This will have to be something that is not privately funded but publicly funded. If it improves our health then it is going to benefit our entire society with less trips to the hospital and a healthier working population.

May 22 2013:
One approach to closing the inequality gap in regards to green space is brownfield restoration. A lot of low income projects are adjacent to abandoned industrial sites can be restored to green space. These spaces often are contaminated and have to be dealt with.The following article gives a great example of this. http://onlinelibrary.wiley.com/doi/10.1111/anti.12009/full

May 22 2013:
I would be interested in seeing any data from New York City comparing rates and appearances of auto-immune disorders of people living in the heart of the city compared with those who live close to Central Park.

May 22 2013:
There was a paper published by Hanski et al. (which we all read for class) http://www.pnas.org/content/109/21/8334.long that correlated auto-immune disorders of kids in houses to the diversity of vegetation surrounding their homes and the diversity of bacteria on their skin (higher plant diversity correlated with higher skin microbiome diversity and lower allergy risk).

What do you think could be done in this type of study that would go beyond correlation? How could we get at mechanism?

May 22 2013:
I think to get at a mechanism we would have to investigate what microbes are associated with asthma and other allergies and auto-immune disorders and if inoculation (or de-inoculation) of any particular strain or set of strains could be found to induce asthma/allergies or another type of auto-immune disorder in mice, or another model system.
Such a study (or more likely set of studies) would predicate upon researchers actually knowing what causes asthma, and I don't know if that's known yet or not.

May 24 2013:
Discover magazine actually mentions the (what I believe to be the aforementioned article in PNAS). It really gets at this idea of being around microbes and plants may contribute to preventing allergies under that the hypersensitivity results from underexposure to microbes, a thought that I and others on this conversation have mentioned: http://blogs.discovermagazine.com/80beats/?p=36985#.UZ_lpJxaT7o.

It is interesting to think that part of what keeps our microbial biome in check actually is the diversity and that the lack of microbial diversity can have a negative impact on our health. Moreover as of late there has been a large push for less use of anti-bacterial soap and antibiotics out of concern of resistant bacteria strands arising.

Another question to consider that is a little off topic is what household products are we using in part to clean as well as reduce our exposure to harmful microbes that may negatively impact the microbial diversity in a household/office environment and in turn people's health.

May 22 2013:
I just think that yes, more research needs to be done (at least for allergies) instead of just correlating low allergy occurrences with living proximity to green spaces. I grew up in the country and have had ridiculous grass allergies my whole life. I also have a friend that grew up in the country that has very bad allergies. There are a lot of factors that could come into play: regional specificity, type of microbes, etc.

Making cities more green is absolutely a great idea in my eyes, but on the allergy side, increasing greenery could increase people's disposition to acquiring an allergy, especially if current research suggests that the urban population has a higher incidence of it.

I know there is a whole lot more involved in this idea but there is my input on the allergy side

May 22 2013:
What about people who work in office buildings or spaces that are sealed with mechanically circulated air? Jessica, Prucia Buscell mentioned your research in her blog "Learning to Tend our Microbial Gardens" (http://www.plexusinstitute.org/blogpost/656763/160814/Learning-to-Tend-Our-Microbial-Gardens) that today's indoor living lifestyle has contributed to a microbial mono-culture, and may in part be associated with asthma and allergies development, what steps do you think can be taken to modify existing building where windows don't open?

Amazon.com is planning on building integrated artificial biomes (greenhouses) to serve as work spaces on their new campus in Seattle. I think if this is successful it could potentially change the way we plan to build in the future. I wonder if these artificial biomes will harbor the same amount of microbial diversity as a natural space?

May 22 2013:
Or, maybe look at stress hormone levels of folks who regularly go to parks and other such green spaces compared to folks who don't. An article in NYT Well section reported that people who live near parks have lower levels of cortisol, a stress hormone, and children with an attention deficit disorder can concentrate better on cognitive tests after walking through a park. A study reported on in the article found that subjects who spent ~25min walking through a park had lower levels of 'brain fatigue' compared to subjects who spent ~25min walking through an urban area. Since the article just reported on differences in stress levels of adults who lived near parks, it would be interesting to see if regularly using parks can be as effective for stress hormones as just living 'near' a park (whatever near means here).
However, most of the information out there seems to point to the huge benefits of access to parks and other green spaces, even if we don't know all the reasons for their benefits, so it seems like we should be planning cities with access to parks in mind.

May 22 2013:
Do you have ideas about how we might tease apart the different mechanisms at play? If stress hormone levels are reduced by spending time in green spaces - how do we figure out what the cause is? How do we know if it is due to the urban microbiome or, for example, a direct impact on physiology/brain function?

May 22 2013:
I like how the CHNA framework uses mapping to visualize relationships between socioeconomic indicators and health outcomes, but what if the spatial scale at which health data is accessible is not the same as the scale at which microbial communities show variation?

May 22 2013:
I just met with someone from Kaiser who told me about the Community Health Needs Assessment http://assessment.communitycommons.org/CHNA/. Right now it sounds like Kaiser is linking physicians up with data from the communities where patients live, for example on airborne particular matter. I am thinking that it would be amazing one day to incorporate data on the urban microbiome with this database, as well as clinical data, to explore the potential links between health and the urban microbiome.

May 22 2013:
This sounds like a great idea to me. It seems challenging to do research that links spatially explicit health data with environmental and microbial data in the U.S. because of the need to protect people's privacy.

May 22 2013:
I haven't really been able to find many longitudinal studies on the link between microbial diversity and human health but that might give us great incite into what microbes are important and how they influence human health.

May 24 2013:
I think that if you look for particular ways microbes may be important and therein by influence human health, e.g. environment and asthma you are more likely to find longitudinal studies. Take for example the study by Arrandale et al. 2011 (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3094407/) who take a look at exposure assessment studies of childhood asthma and look at ways to improve future exposure assessment studies. One reason for carrying about the quality of such assessments is that longitudinal studies are quite costly and time intensive. The Urban Environment and Childhood Asthma (UREA) is a study by Gern et al. (2011) http://www.biomedcentral.com/1471-2466/9/17 specifically studies what immune responses trigger asthma in inner-city children. They looked at children from birth until age 7 for the following cities: Baltimore, Boston, New York City, and St. Louis. That study was collecting data for 7 years before being able to fully analyze the data. Longitudinal data once is created is great and can be very insightful, however it takes time to compile and thus can kind of be like a "hail mary" for researchers to invest in such a gamble of a research project.

May 22 2013:
This could be a good way to get more information about the the negative effects of pollution. Maybe a(nother) problem with air pollution is that it decreases the diversity of airborne microbes or the abundance of 'good' microbes.

May 24 2013:
I have been trying to find a paper on the effects of air pollution on microbial diversity but haven't found anything yet. I did find this paper that talk about the effect of indoor air pollution on health http://www.jmsmd.net/images/Indoor_Air_Pollution_Health_Effects.pdf. It only mentions microbes very briefly but does say that some of these pollutants can kill microbes. With a population that is increasing its time spent indoor it will be important to improve air quality both indoors and outdoors.

May 24 2013:
Your point about time spent indoors is important. In the U.S., we spend over 90% of our lives inside buildings [http://energy.lbl.gov/ied/pdf/LBNL-47713.pdf], so researchers have been looking at indoor air quality a lot. I think something that has been less studied is the strength of the link between indoors and outdoors, and how the quality of the immediate outdoor context might influence indoor air generally and airborne microbes specifically. Studies have shown that indoor airborne microbial communities tend to be similar to outdoor airborne microbial communities in buildings that ventilate with outdoor air, like buildings designed to use natural ventilation and many residences that lack a/c [for example, http://onlinelibrary.wiley.com/doi/10.1111/ina.12047/abstract]. It is less clear how the dominant airborne microbial communities in the immediate vicinity vary by neighborhood characteristics and over time.

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